The present invention relates to the specific field of turbomachines, and more particularly it relates to the problem posed by mounting a metal end wall for a turbomachine combustion chamber on the side walls of said chamber when the side walls are made of ceramic matrix composite (CMC) type material.
Conventionally, in a turbojet or a turboprop, the high pressure turbine (HPT), and in particular its inlet nozzle, the injection system, the combustion chamber, and the annular shell of said chamber are all made of metal type materials. However, under certain particular conditions of use employing particularly high combustion temperatures, a combustion chamber that is made entirely out of metal is completely unsuitable from a thermal point of view and it is necessary to use a chamber based on high temperature composite materials of the CMC type. However, the difficulties involved in working these materials and their high costs mean that use of such materials is usually restricted to the combustion chamber itself and more particularly solely to its axially-extending side walls, with the inlet nozzle of the high pressure turbine, the injection system, and the annular shell continuing to be made more conventionally out of metal materials. Unfortunately, metal materials and composite materials have coefficients of thermal expansion that are very different. This gives rise to problems that are particularly severe at the connections between the composite material side walls of the combustion chamber and its metal end wall.
The present invention mitigates those drawbacks by proposing a mounting for a metal end wall of a combustion chamber that has the ability to absorb the movements induced by the different coefficients of expansion between said metal end wall and the composite side walls of the combustion chamber.
These objects are achieved by an annular combustion chamber having outer and inner axially-extending side walls of composite material and an end wall of metal material, wherein, in order to enable said end wall to expand freely in a radial direction relative to said side walls, said end wall is held in position between said inner and outer side walls by a plurality of flexible tongues fixed firstly to said side walls by fixing means and secondly to said end wall by brazing or welding, said end wall further including means for providing sealing between said end wall and said side walls.
With this fixing system based on flexible tongues, expansion of the metal end wall of the chamber is absorbed without damaging the composite material side walls. The tongues can accommodate the forces due to the large amount of expansion of the end wall without stressing the side walls which, in contrast, expand little.
The flexible fixing tongues are made of a metal material and the fixing means are constituted by a plurality of bolts, preferably having captive nuts.
In an embodiment, the sealing means comprise a circular gasket of the laminated type mounted in a circular groove of said metal end wall of the chamber and designed to bear against the facing one of said side walls of the combustion chamber. The circular gasket is preferably subdivided into sectors and is held pressed against said side wall by means of a resilient element fixed on said metal end wall. The resilient element is constituted by spring blades.
In an alternative embodiment, the sealing means comprise a circular segment mounted against said side wall and designed to co-operate with a circular groove in said metal end wall of the chamber. The circular sealing segment is preferably split.
In an advantageous embodiment, the flexible fixing tongues have respective first ends fixed to one or other of said side walls by said fixing means and respective second ends fixed to said end wall of the combustion chamber by brazing or welding. Under such circumstances, the end wall can also have a metal ring onto which the second end of said flexible fixing tongues are brazed or welded.
In another embodiment, the flexible fixing tongues have respective first ends fixed to one of said side walls by first connection means and respective second ends fixed to the other one of said side walls by second connection means, together with respective central portions fixed to the end wall by brazing or welding. Advantageously, the flexible fixing tongues are disposed between successive injection nozzles.